Our very strange 12V battery system

[dmd3home]

So I've been paying close attention to my 12v battery which certainly seems a weak point in our trucks. To minimize problems, I, like many, keep the battery on a maintainer when it's not being driven. To monitor even more precisely, I've added a VOM voltmeter. In watching this voltmeter in various situations I've observed some strange results. Normally you'd see a fairly steady 14.5v or so but in this situation I had the maintainer off (unplugged) and I was charging the truck's HV battery via a level one 120V solar/battery/inverter system. As you see, the 12V battery voltage varies wildly...with values of less than 1V to about 14.5V. At first I thought my voltmeter was failing me so I tried another....same thing. I was measuring the voltage directly off the battery posts so I thought perhaps I needed to measure downstream of the battery BMS. But, trying this produced the same result. But, when disconnecting from the level one charging, the 12V battery voltage shows a more normal and stable 12.5V to 14V. It obviously the had something to do with charging the truck

Why would the measured voltage have such swings? What is really happening here? Logic would suggest that the only way the measured voltage could momentarily drop to less than one volt would be to have a high load on it. But that wasn't the case. The 12v battery, although quite small, should provide a relatively stable voltage under any condition. Strange! Are there some added high frequency pulses to the 12v battery that are fooling my meter? Strange!

Sponsored

 

[hturnerfamily]

what's interesting, at least in my situation, with one of the original PRO SR, with the 100kwh battery pack, I have yet to change the 12v 'starter' battery, or, actually, have a SINGLE ISSUE with it, after over 71,000 miles.... with MANY, MANY hours of ProPower usage, for various reasons, mainly when towing our camper over 25,000 miles and powering the camper WHILE in motion, to keep the fridge operating, fans runnings, devices powered, and even having the overhead roof Air Conditioner running(or on thermostat)... and several instances of powering our home during an outage, or charging our other EV, the Kia EV9, or while using ProPower overnight, with the truck ON the whole time... etc.
And, recently, while kyaking quite a bit in our local river, LEAVING THE TRUCK ON the whole time, to keep the air conditioner cooling, during these HOTT, and maybe more important, HUMIDD(!) days...
if the truck shuts off while on the river, I simply use the Ford APP to turn on the 'CLIMATE', and EXTEND the time, for the truck to remain COOL until we return. It has worked flawlessly.(I will say that Ford annoyingly limits the ability to 'cool'[Remote Climate Control] from the App more than once, for some unknown 'reason'... but, I have also noticed that if you have received the "you have 30 seconds until the truck turns off" message, and press the OK button to defeat that, the truck will actually REMAIN ON, well, I guess, forever... I've used this also for the purpose of keeping the truck ON, overnight, so that ProPower can remain on and active the whole time)

so, after all that said: is it time to CHECK the 12v Battery, and maybe REPLACE it?

maybe...



maybe not.


See ya in the funny papers.

for GEORGIA Ford F150 LIGHTNING owners...text : 2299379150
or DirectMessage me... William

 

[ZSC100]

When the vehicle is ON the DCDC will float charge the 12V battery to 14V+. Just like an alternator would in a normal ICE car. While actively charging (any level) the DCDC also maintains the 12V battery. So, the 12V battery is being maintained most all the time, held above 90% SoC. There is no need to add any aftermarket charger of any kind to the truck, unless the truck will be sitting completely unattended for a LONG Time. Imagine buying an $80k truck then thinking you need to add a trickle charger to it like the engineers didn't think of that? It's sad but that's exactly what has happened due to poor quality and size of 12V battery they put in these trucks.

Another thing Ford does terrible on is education for Owners. So, just becaues a charger is plugged in doesn't mean anything, an active charge session has to be happening for the DCDC to be on. Once the on board charger reaches it's setpoint everything shuts off even if the EVSE remains plugged in. This is something that isn't really told anywhere to my knowledge.

 

[Adventureboy]

The low spikes are not normal. First, make sure your battery connectors are clean and tight. A drop to <1v would normally shut the truck down. As @hturnerfamily said, check the 12v battery health. I'm on number 3 on my 2023 Lariat.

With the Frunk open, it will keep modules live and could be doing some goofy things. Try running leads outside the closed frunk and take readings an hour after you shut down and plug in (leave phone/fob in the house so it doesn't light things up).

I don't use L1, however, my 2023 Lariat stays flat at around 15v while plugged in and actively charging the HVB.

Incidentally, I have swapped to H4 and haven't needed to use my trickle charger since (it is summer, so that's a factor)

 

[Adventureboy]

There is no need to add any aftermarket charger of any kind to the truck, unless the truck will be sitting completely unattended for a LONG Time.

There are exceptions to this. A couple of driveway shuffles and/or short drives to the corner store will leave the 12v battery in a low SOC. The truck will charge the 12v when it drops below 50% SOC however, if you do this daily, it will kill the 12v battery prematurely by repeatedly discharging it below 50%. A trickle charger solves this, and improves the longevity of the 12v. Agree it shouldn't be needed on our trucks, but if your drive patterns match the above, it is.

 

[chl]

So I've been paying close attention to my 12v battery which certainly seems a weak point in our trucks. To minimize problems, I, like many, keep the battery on a maintainer when it's not being driven. To monitor even more precisely, I've added a VOM voltmeter. In watching this voltmeter in various situations I've observed some strange results. Normally you'd see a fairly steady 14.5v or so but in this situation I had the maintainer off (unplugged) and I was charging the truck's HV battery via a level one 120V solar/battery/inverter system. As you see, the 12V battery voltage varies wildly...with values of less than 1V to about 14.5V. At first I thought my voltmeter was failing me so I tried another....same thing. I was measuring the voltage directly off the battery posts so I thought perhaps I needed to measure downstream of the battery BMS. But, trying this produced the same result. But, when disconnecting from the level one charging, the 12V battery voltage shows a more normal and stable 12.5V to 14V. It obviously the had something to do with charging the truck

Why would the measured voltage have such swings? What is really happening here? Logic would suggest that the only way the measured voltage could momentarily drop to less than one volt would be to have a high load on it. But that wasn't the case. The 12v battery, although quite small, should provide a relatively stable voltage under any condition. Strange! Are there some added high frequency pulses to the 12v battery that are fooling my meter? Strange!

Maybe you have an analog meter?
Try that.

Digital multi-meters will 'hunt' for the voltage if it is changing even a tad, which drives me crazy sometimes, so I stick with analog meters.

I think THAT is what you are observing.

If your 12v went down to 1v in actuality, it would be a dead parrot, it would be no more, deceased, gone to it's final resting place, etc.

 

[dmd3home]

Yes, as I was saying, if the voltage actually dropped below 1 volt, that would indicate an incredible load....dead short, and there would be other, extreme indicators. However, it's still odd that it's only when I'm charging the HV battery. I do think I still have an analog meter around here somewhere. I'll further investigate.
BTW, I did get the PPOB with truck off update yesterday and it's great. Thanks Ford. Though I do wish the setting would stay and not have to be reselected each time. Still, I'm quite impressed that Ford did this update for older trucks and on a vehicle they no longer make or sell.....good on them!

 

[chl]

Yes, as I was saying, if the voltage actually dropped below 1 volt, that would indicate an incredible load....dead short, and there would be other, extreme indicators. However, it's still odd that it's only when I'm charging the HV battery. I do think I still have an analog meter around here somewhere. I'll further investigate.
BTW, I did get the PPOB with truck off update yesterday and it's great. Thanks Ford. Though I do wish the setting would stay and not have to be reselected each time. Still, I'm quite impressed that Ford did this update for older trucks and on a vehicle they no longer make or sell.....good on them!

When charging the 12v battery is being used to close the contactors (and hold them closed?) so the charge port is connected to the HVB via the AC-DC converter. Some of that charging juice is being used/diverted to maintain the 12v battery via the DC-DC converter, so...the 12v battery voltage is going to vary somewhat while charging.

Besides the voltage fluctuations due to the use of the 12v battery, digital systems are sampling constantly and slight variations in resistance or noise voltage causes the hunting effect. When charging, the AC-DC converter is likely producing electrical noise.

BTW with a L1 charge, probably less available for the 12v battery or anything else. And in winter, the L1 may not add much to the HVB because it also is being used to precondition and warm the battery if below about 40 degrees ambient (as I recall, details, details...). Noise will be more prominent when the line voltage is 120v vs 240v L2.

Anyway I don't often use my digital multi-meter anymore with DC voltage measurements because of the hunting effect.

 

[chl]

PS I should also have mentioned that DC-DC step down converters produce pulsed DC output that is then filtered, but no filtering is perfect so when the 12v battery is being charged/maintained there will be slight fluctuations and if your meter is sensitive enough it will pick them up and 'hunt.'

In the Lightning to step down the HVB DC to 12V (actually around 14vdc) is probably using switching to step it down which doesn't waste energy but does produce noise that has to be filtered.

Bottom line is there are lots of potential sources of 'noise' to drive a digital multi-meter crazy!

Sponsored